Re: [PATCH 2/6] virtio: virtqueue_pop - VIRTIO_F_IN_ORDER support

[Eugenio Perez Martin]

On Mon, May 6, 2024 at 5:06 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
> Add VIRTIO_F_IN_ORDER feature support in virtqueue_split_pop and
> virtqueue_packed_pop.
>
> VirtQueueElements popped from the available/descritpor ring are added to
> the VirtQueue's used_elems array in-order and in the same fashion as
> they would be added the used and descriptor rings, respectively.
>
> This will allow us to keep track of the current order, what elements
> have been written, as well as an element's essential data after being
> processed.
>
> Tested-by: Lei Yang <leiyang@redhat.com>
> Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> ---
>  hw/virtio/virtio.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 893a072c9d..e6eb1bb453 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1506,7 +1506,7 @@ static void *virtqueue_alloc_element(size_t sz, 
> unsigned out_num, unsigned in_nu
>
>  static void *virtqueue_split_pop(VirtQueue *vq, size_t sz)
>  {
> -    unsigned int i, head, max;
> +    unsigned int i, j, head, max;
>      VRingMemoryRegionCaches *caches;
>      MemoryRegionCache indirect_desc_cache;
>      MemoryRegionCache *desc_cache;
> @@ -1539,6 +1539,8 @@ static void *virtqueue_split_pop(VirtQueue *vq, size_t 
> sz)
>          goto done;
>      }
>
> +    j = vq->last_avail_idx;
> +
>      if (!virtqueue_get_head(vq, vq->last_avail_idx++, &head)) {
>          goto done;
>      }
> @@ -1630,6 +1632,12 @@ static void *virtqueue_split_pop(VirtQueue *vq, size_t 
> sz)
>          elem->in_sg[i] = iov[out_num + i];
>      }
>
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_IN_ORDER)) {
> +        vq->used_elems[j].index = elem->index;
> +        vq->used_elems[j].len = elem->len;
> +        vq->used_elems[j].ndescs = elem->ndescs;
> +    }
> +
>      vq->inuse++;
>
>      trace_virtqueue_pop(vq, elem, elem->in_num, elem->out_num);
> @@ -1758,6 +1766,13 @@ static void *virtqueue_packed_pop(VirtQueue *vq, 
> size_t sz)
>
>      elem->index = id;
>      elem->ndescs = (desc_cache == &indirect_desc_cache) ? 1 : elem_entries;
> +
> +    if (virtio_vdev_has_feature(vdev, VIRTIO_F_IN_ORDER)) {
> +        vq->used_elems[vq->last_avail_idx].index = elem->index;
> +        vq->used_elems[vq->last_avail_idx].len = elem->len;
> +        vq->used_elems[vq->last_avail_idx].ndescs = elem->ndescs;
> +    }
> +

I suggest using a consistent style between packed and split: Either
always use vq->last_avail_idx or j. If you use j, please rename to
something more related to the usage, as j is usually for iterations.

In my opinion I think vq->last_avail_idx is better.


>      vq->last_avail_idx += elem->ndescs;
>      vq->inuse += elem->ndescs;
>
> --
> 2.39.3
>